This invention relates to the telephone transmitter portion of a telephone handset and is concerned with reducing wide-noise produced by an undesired air stream blowing into the transmitter-microphone.
Conventionally, several types of microphones have been used in telephone-transmitters, including dynamic microphones and carbon microphones. Such prior art microphones, however, have disadvantages. For example, the dynamic type microphone is costly and complicated in construction. The carbon microphone is also costly, has a narrow bandwidth but a relatively high output voltage, has its peak frequency response at a frequency above the necessary audible range, is unstable in operation, and is relatively noisy. With recent advances in transmission techniques, other types of microphones such as the electret condenser microphone are being considered for use in telephone transmitters. The electret condenser microphone is both low in cost and has a good frequency characteristic.
Microphones such as the electret condenser type, however, have a low mechanical impedence for the vibrating membrane therein and a frequency response characteristic including the low frequency region, ofter as low as several tens of hertz. Because of these characteristics, means must be provided to minimize pick-up of undesired low frequency wind-noise produced, for example, by the air stream which accompanies breathing and speaking of a talker. Because of the relatively poor low frequency response of prior art microphones, this problem has not previously received widespread attention.